Wire Sizing Help Please

[dspizzle]

So I have researched many different peoples setups and everyone does it a little different. Here is my thoughts on a setup.

Need major advice on the wire sizing please.

P.S. I have read HandyBobsSolar. Planning to read again this weekend after putting this together.

[john61ct]

Use the Circuit Wizard app from Blue Seas.

Ask here if you don't understand any of the factors, very educational. Double distance for the round trip.

And Bob's great, but a bit over-committed in some hobby horse fixations and now a bit outdated.

[Twigg]

Originally Posted by john61ct

Use the Circuit Wizard app from Blue Seas.

Ask here if you don't understand any of the factors, very educational. Double distance for the round trip.

And Bob's great, but a bit over-committed in some hobby horse fixations and now a bit outdated.

Distilling the parts where Bob is still accurate can be tricky.

I'd pay very close attention to his comments on battery charging and monitoring though.

[dspizzle]

How does the setup look overall?

[dspizzle]

Trying to get this stuff purchased and installed asap.

[roach711]

I would use 10ga for the breaker panel to inverter run. 12ga is fine for 20amps but with multiple 120v circuits you may be drawing well in excess of that. 10ga is fine for your 30amp service and with the same gauge running to the panel there would never be a chance to overload that run.

I'm not a solar expert but 16ga running from the panels to the charge controller looks way small. Most articles I've read recommend going oversize on that run to compensate for voltage loss through cable resistance. You never go wrong by going too big on wiring, particularly in DC circuits.

[dspizzle]

Originally Posted by roach711

I would use 10ga for the breaker panel to inverter run. 12ga is fine for 20amps but with multiple 120v circuits you may be drawing well in excess of that. 10ga is fine for your 30amp service and with the same gauge running to the panel there would never be a chance to overload that run.

I'm not a solar expert but 16ga running from the panels to the charge controller looks way small. Most articles I've read recommend going oversize on that run to compensate for voltage loss through cable resistance. You never go wrong by going too big on wiring, particularly in DC circuits.

Heard on the 10 ga for sure. 16 ga was what a voltage calculator pumped out for only a 2% voltage drop. I think it is because the voltage is high in that wire and the load is very small. But I might bump it up a size based on how long my run ends up being.

[dspizzle]

Is there any need to run a 50 amp service if I'm not running a rooftop ac?
Not planning to be plugged in very often, if ever.

[Iceni John]

Several things make me nervous, or at least curious, about your plan.
1. Why connect your panels in series? If one panel is shaded, you'll lose all your power. Parallel tolerates shading, leaves and dirt, bird poop, etc better than series. It's not like you need to save cable for the short distances on a bus, so using 10AWG feeders from each panel to a combiner (with 15A fuses for each panel), then a heavy but short downfeed cable to the CC, makes more sense.
2. Running almost 160V into a 150V CC is asking for trouble. And what will you do on a cold clear winter day, or an edge-of-cloud event?
3. Input to and output from the CC should have breakers for ease of disconnecting. Carling Type C breakers are available for both DC and AC and they're very compact, so they're a good choice everywhere in a bus. They should be sized for the NEC's 125% cushion. Square D QO breakers are hardly the best for a bus or boat - what do you think Blue Sea and Paneltronics use for their high-$$$ marine load centers?
4. Fuses and CBs protect wiring, not loads. WTH size cable are you protecting with a 400A fuse??? 250MCM? (I have a Magnum MS2000 running off 12V, and it has a 250A ANL fuse for its 4/0 feed cable.)
5. And if you were to pull almost 400A from a 660aH battery bank you would get so much voltage droop that the inverter's LVD would probably trip, or you'd probably fry its MOSFETs. For that size inverter you need more battery aH, which in turn needs more PV if you want to charge at the upper end of FLA batteries' recommended 5-13% charge rate. The larger the inverter, the greater its standby current drain: don't use a larger inverter than necessary, otherwise it will use half your PV power just being on!
6. You should think of having a catastrophe fuse for the battery bank, ideally on the negative. (I use 300A Class T catastrophe fuses for each of my banks' outputs, not cheap but very quick-acting.) These are NOT load fuses which should still be on each battery pair's outputs.

Remember, even a PV system can easily produce more than enough power to kill you or start a serious fire, so you need to think through everything very carefully. I recommend you read the NAWS forum thoroughly and learn from the collective wisdom there - those guys are the real solar gurus!

Back to your original question about wire size. Easy! Go big. See, that was easy. If in doubt, go bigger than NEC, and a lot bigger if it's in conduit. And PLEASE don't use those goddam hammer crimpers - they're crap. Use a proper circumferential crimper like the FTZ 94284, and a good cable cutter like a long-handled Temco, and tin-plated lugs, and good heatshrink, then you'll be OK.

John

[john61ct]

https://marinehowto.com/marine-wire-termination

https://marinehowto.com/making-your-own-battery-cables/

Everything at the site about electrickery well worth reading, and help support him by buying from him, even if it costs a bit more, all top quality gear.

[2martins]

Do you need to go larger in co suit because of heat build up? Does using the kind with holes help? Is it better NOT to use conduit unless its under the bus to protect it? I know nothing!!! I liked the idea of conduit to protect the wires from rubbing, mice, etc.

Originally Posted by Iceni John

Several things make me nervous, or at least curious, about your plan.
1. Why connect your panels in series? If one panel is shaded, you'll lose all your power. Parallel tolerates shading, leaves and dirt, bird poop, etc better than series. It's not like you need to save cable for the short distances on a bus, so using 10AWG feeders from each panel to a combiner (with 15A fuses for each panel), then a heavy but short downfeed cable to the CC, makes more sense.
2. Running almost 160V into a 150V CC is asking for trouble. And what will you do on a cold clear winter day, or an edge-of-cloud event?
3. Input to and output from the CC should have breakers for ease of disconnecting. Carling Type C breakers are available for both DC and AC and they're very compact, so they're a good choice everywhere in a bus. They should be sized for the NEC's 125% cushion. Square D QO breakers are hardly the best for a bus or boat - what do you think Blue Sea and Paneltronics use for their high-$$$ marine load centers?
4. Fuses and CBs protect wiring, not loads. WTH size cable are you protecting with a 400A fuse??? 250MCM? (I have a Magnum MS2000 running off 12V, and it has a 250A ANL fuse for its 4/0 feed cable.)
5. And if you were to pull almost 400A from a 660aH battery bank you would get so much voltage droop that the inverter's LVD would probably trip, or you'd probably fry its MOSFETs. For that size inverter you need more battery aH, which in turn needs more PV if you want to charge at the upper end of FLA batteries' recommended 5-13% charge rate. The larger the inverter, the greater its standby current drain: don't use a larger inverter than necessary, otherwise it will use half your PV power just being on!
6. You should think of having a catastrophe fuse for the battery bank, ideally on the negative. (I use 300A Class T catastrophe fuses for each of my banks' outputs, not cheap but very quick-acting.) These are NOT load fuses which should still be on each battery pair's outputs.

Remember, even a PV system can easily produce more than enough power to kill you or start a serious fire, so you need to think through everything very carefully. I recommend you read the NAWS forum thoroughly and learn from the collective wisdom there - those guys are the real solar gurus!

Back to your original question about wire size. Easy! Go big. See, that was easy. If in doubt, go bigger than NEC, and a lot bigger if it's in conduit. And PLEASE don't use those goddam hammer crimpers - they're crap. Use a proper circumferential crimper like the FTZ 94284, and a good cable cutter like a long-handled Temco, and tin-plated lugs, and good heatshrink, then you'll be OK.

John